Photographic black-and-white silver halide photosensitive materials are generally processed through steps of development, fixation, and water washing. This type of processing, presents problems relating to environmental protection and water conservation.
One approach to minimizing environmental effects is to reduce the necessary amount of wash water which has been used in processing 3 to 20 liters of wash water per square meter of photosensitive film is typical. For example, counter current washing through a plurality of wash tanks is disclosed in S. R. Goldwasser, "Water flow rate in immersion-washing of motion picture film," J. SMPTE, 64, 248-253, May 1955. This technique is commonly used to reduce wash water volumes in automatic processors for photographic color film.
In automatic processors for x-ray photosensitive film, it is now common to conserve water as much as possible by opening an electromagnetic valve to supply wash water only during a processing period. If the multiple-tank counter current washing technique is applied to automatic processors for sheet photosensitive material such as x-ray photosensitive film and printing photosensitive material, a number of rollers and racks corresponding to the number of wash tanks must be utilized, adding to push the initial cost of the automatic processor beyond a commercially acceptable level and increasing the space for the installation thereof.
Therefore, most automatic processors for processing sheet black-and-white photosensitive material depend on the conventional mass water washing mode wherein the processor is equipped with a single wash tank, or primary and auxiliary wash tanks, or at most double wash tanks. In such a system at least 3 liters per square meter of the photosensitive material of wash water is replenished.
Often wash water is kept for some time in a wash tank. Then bio-slime will adhere to the tank wall within 2 or 3 weeks and the water will stagnate or rot giving off foul odors. When the automatic processor is turned off and discontinued for several days, suspended matter will appear in the water in the wash tank. Such suspended matter will eventually adhere to a photosensitive material or cause clogging of associated filters. Therefore, the wash tank must be periodically scrubbed to remove bio-slime and suspended matter. When bio-slime accumulates on a roller conveyor system which includes a number of moving components, scrubbing the rollers and racks to remove the bio-slime is a cumbersome operation.
For bio-slime control, it was a common practice to add chelating agents and biocidal agents to wash water as disclosed in L. E. West, Water Quality Criteria Phot. Sci. and Eng., Vol. 9, No. 6, 398 (1965); M. E. Beach, "Microbiological growth in Motion-Picture Processing," SMPTE Journal, Vol. 85, Mar. 1976; and R. O. Deegan, "Photoprocessing Wash Water Biocides," J. Imaging Tech., Vol. 10, No. 6, Dec. 1984. Also, Japanese Patent Application Unexamined Publication (JP-A) Nos. 8542/1982, 105145/1983, and 157244/1982 disclose the addition of various antifungal agents such as thiazolylbenzimidazoles and isothiazolones. Although the concept of adding a biocidal or fungicidal compound to wash water is helpful, the mass water washing mode, however, makes it difficult to maintain the compound at an effective concentration so as to provide biocidal and fungicidal action. In addition, some chemical agents are costly and some are toxic. No satisfactory method of bio-slime prevention has previously been achieved.